JPH03116547A - Information recording and reproducing device - Google Patents

Abstract

PURPOSE:To miniaturize an optical head, to simplify assembly and adjustment and to stably detect a light beam by providing a non-polarizing reflection surface on a transmission means and turning a light beam from a light source toward a focusing means through the reflection surface. CONSTITUTION:A non-polarizing light beam split surface (m) is used as a separation means for the light beam generated from a semiconductor laser element 2 and the plane of polarization of the light beam generated from the laser element 2 is rotated by about 45 deg., for example, against the reference axis included in a plane parallel with a direction where the light beam is transmitted on the polarizing light beam split surface for separating the light beam and making it incident on photodetectors 26 and 28, that is, a Y-axis. Therefore, the device has stable characteristic with simple constitution and the assembly and the adjustment can be possible. Furthermore, the optical path of the light beam from the laser element 2 is bent to be parallel with an optical disk 12 being an information recording medium by a non-polarizing reflection surface (m). Thus, the miniaturized optical head whose thickness is thin is obtained.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an optical head incorporated in an optical information recording/reproducing device such as an optical disk device, and particularly relates to an optical head incorporated in an optical information recording/reproducing device such as an optical disk device. The present invention relates to an optical head for recording, reproducing, or erasing information on an optical head.

(Prior Art) In an optical information recording and reproducing device, for example, an optical disk device, information is recorded on an optical recording medium, that is, an optical disk, and an optical head is used to reproduce the information from the optical disk. .

In such an optical head, a light beam generated from a semiconductor laser element as a light source is focused onto an optical disk by an objective lens inside the optical head, and a light beam reflected from the optical disk is guided to a photodetector. is detected and converted into a playback signal. When reproducing and recording information on an optical disk, the objective lens is maintained in a focused state so that the beam waist of the light beam, that is, the minimum beam spot is formed on the optical disk, and the objective lens is maintained in a focused track state. Tracks formed on the optical disc are tracked by a light beam to accurately record and reproduce information on the optical disc. As optical heads used in the above-mentioned optical disk devices, optical heads for write-once optical disks, optical heads for magneto-optical optical disks, and the like are known.

In a magneto-optical optical disk head, information is recorded, reproduced, and erased using a light beam irradiated onto the recording surface of an optical disk and a magneto-optical effect. This optical head includes a focusing means that focuses a light beam generated from a semiconductor laser element as a light source onto the information recording surface of an optical disk, and a light beam that directs reflected light from the optical disk to a photodetector that is a signal detection means. It consists of a beam separating means and a photodetector for detecting the separated light beam and using it as a focusing control signal, a tracking control signal, and an information reproduction signal. In this magneto-optical optical disk optical head, light emitted from a semiconductor laser has a polarization plane in a direction perpendicular to an optical axis parallel to the recording surface of an information recording medium, that is, an optical disk, and has an elliptical cross-sectional shape. The beam is focused onto an optical disk via an ellipse correcting refractor, a separating means or prism, and an objective lens.

This light beam is generated with a constant intensity when reproducing information, and is generated with intensity modulated according to the information when recording.

Furthermore, during erasing, the signal is generated at a constant intensity that is greater than during reproduction. When recording information on an optical disk, a magnetic field is applied from a magnet placed on the side of the optical disk facing the optical head, and the direction of magnetization of the area irradiated with the light beam is changed to record information. When erasing information, a magnetic field is applied in the same manner as during recording, and the direction of magnetization of the region irradiated with the light beam is changed again (returned to its original state). When reproducing information, the light beam is changed depending on the information recorded on the optical disc. That is, when no information is recorded on the optical disc, the light beam is reflected as is, and when information is recorded, the polarization plane of the light beam is slightly rotated. The light beam reflected from the optical disk is returned to parallel light by the objective lens, and is separated from the light beam traveling from the light source to the information recording medium via the separating means.

This separated light beam is separated into two light beams by a focus detection light beam separation means, one of the light beams is guided to a focus detection photodetector, and the other light beam has a polarization plane of 45. The plane of polarization is rotated by 45'' via a rotating 1/2λ plate, guided to a polarizing beam splitter, and further separated into a P polarized light component that passes through the beam splitter and an S polarized light component that is reflected by the beam splitter.

Each of the further separated P-polarized light component and S-polarized light component is detected by two photodetectors, and the information recorded on the optical disc is reproduced. When reproducing information,
Normally, when there is no recorded information, the 1/2 λ plate is rotated and adjusted so that the P-polarized light component and the S-polarized light component are equal, and if there is a difference between the outputs of the two photodetectors, it is output as an information signal. information is played back.

Therefore, in such an optical head, with respect to the rotation of the polarization plane of the light beam around the optical axis of the light beam,
A 172-wave plate for increasing the stability of reproduced signals and a rotation adjustment machine configuration or semiconductor laser element that adjusts the rotation of the light beam of the 1/2 wavelength plate with respect to the optical axis in response to the difference in the polarization plane of the individual semiconductor lasers. Additional devices are provided, such as a rotation mechanism for rotating 2.

(Problems to be Solved by the Invention) In the optical head described above, as described above, there is a method for increasing the stability of the reproduced signal with respect to rotation of the polarization plane of the light beam around the optical axis of the light beam. Additional devices such as a rotation adjustment mechanism for adjusting the rotation of the light beam of the 1/2 wavelength plate with respect to the optical axis due to the difference in the polarization plane of the 1/2 wavelength plate and the individual semiconductor lasers are required to form the optical head. The number of parts for the optical member increases. In such an optical head, the increase in the number of optical members complicates the assembly and adjustment of the device, making the device larger and heavier, reducing the stability in detecting and reproducing information signals, and reducing the durability of the device. There is a problem in that not only does it cause deterioration, but also an increase in cost.

An object of the present invention is to provide an optical head that can prevent a decrease in the S/N ratio of a reproduced signal, reduce the size of the optical head, simplify assembly and adjustment, and stably detect a light beam. shall be.

[Structure of the Invention] (Means for Solving the Problems) The present invention has been made based on the above-mentioned problems, and includes a light source that generates a light beam having a plane of polarization, and a system that uses information about the light beam generated from the light source. An information recording and reproducing device comprising a transmission means for guiding the light beam to a recording medium, a focusing means for focusing the light beam on the information recording medium, and a means for separating the light beam from the information recording medium into at least two light beams. wherein the plane of polarization of the light beam from the light source forms a predetermined angle with respect to a reference axis on the light source with respect to the polarization direction of the light beam separated by the separation means, and the transmission means:
The present invention provides an information recording and reproducing device characterized in that it has a non-polarizing reflective surface, and a light beam from the light source is directed to the focusing means via the reflective surface.

(Function) According to the optical head of the present invention, a non-polarizing beam splitting surface is used as a means for separating the light beam generated from the semiconductor laser element.

Therefore, the polarization plane of the light beam generated from the semiconductor laser element is the reference axis included in the plane parallel to the direction in which the light beam is transmitted on the polarizing beam split surface that separates the light beam and makes it incident on the photodetector. i.e. approximately 45 to the Y axis
``Because it is rotated, the 1/2 λ plate for keeping the transmittance of the P-polarized light component and the reflectance of the S-polarized light component of the light beam constant and the rotation adjustment mechanism that adjusts the rotation of the light beam with respect to the optical axis are removed. This makes it possible to provide an optical head that has a simple structure, stable characteristics, and can be assembled and adjusted.Furthermore, the non-polarizing reflective surface allows the optical path of the light beam from the semiconductor laser element to be aligned with the information recording medium. By bending the optical head parallel to the optical disk, a thin and compact optical head is provided.

(Embodiment) FIGS. 1A and 1B show an optical head that is incorporated into an erasable magneto-optical optical disc device that is an embodiment of the present invention. FIG. 1A schematically shows the arrangement of the components of the optical head, and FIG. 1B shows the optical head shown in FIG. 1A in a plan view.

In this optical system, it is assumed that a light source that generates a light beam having a polarization plane, that is, the semiconductor laser element 2, has an elliptical cross-sectional shape and that the polarization plane is image-formed on the reference axis, that is, the reference axis is projected. A pre-beam is generated which is rotated approximately 45° with respect to the reference axis or Y-axis of the separation means, which is polarized along the corresponding direction so that the shadow is displaced. Furthermore, a non-polarizing beam splitter is used as the beam splitter 6 that transmits or reflects the light beam from the semiconductor laser element 2, and the reflecting mirror m formed on one surface of the joined prism 18 is a non-polarizing mirror. is used.

Conventionally used polarizing beam splitters and polarizing mirrors transmit the linearly polarized light component (P polarized light component) on the plane parallel to the polarizer on the beam splitting surface, and transmit the linearly polarized light component (S polarized light component) on the plane perpendicular to the polarizer. In contrast, the non-polarizing beam splitter and non-polarizing mirror do not have a polarizer and reflect almost all the P-polarized light components and S-polarized light components of the light beam generated from the semiconductor laser element 2. Transmit or reflect an equal amount. A light beam with an elliptical cross section generated from the semiconductor laser element 2 is converted into parallel light by a collimator lens 4, and is converted into a substantially circular cross-sectional shape equal to the short axis diameter of the ellipse by an incident light limiting means, which will be described later. The beam is restricted and incident on the first beam splitter 6. The light beam transmitted through the beam splitter 6 is reflected by the reflecting surface m, which is a non-polarizing beam split surface formed on one surface of the prism 18 joined to the beam splitter 6 via the beam splitter surface 8, and is reflected by the objective lens. Guided by 20. The light beam guided to the objective lens 2o is directed to an optical disk 12J), which has a recording layer made of an amorphous magnetic alloy or the like, and has concentric or spiral tracks 14 formed in a concave or convex shape. It is focused onto the rack 14. The track 14 is pre-formatted with preliminary information such as a track address and a sector address. Information is recorded on the track 14, and information is reproduced and erased from the track 14 by a method of changing the intensity of the light beam, which will be described later. The light beam reflected from the optical disk 12 is returned to the beam splitter 6 via the objective lens 20 and the reflective surface m of the prism 18. This light beam is reflected by the beam splitting surface 8 of the beam splitter 6 and enters the second beam splitter 70. The light beam is split into two beams by the polarization beam splitting surface of the beam splitter 70, and one beam is guided to the first photodetector 26 via the TTP 22 as a focus detection light beam. The other light beam is split into S by a polarizing beam splitter 90.
The light beams are separated into a polarized light component and a P-polarized light component, and each light beam is guided to second and third photodetectors 27 and 28, detected, and electrically processed to reproduce information.

In the optical head shown in FIGS. 1A and 1B, when there is no information recorded on the optical disk 12, the light beams detected by the two photodetectors 27 and 28 need to be made equal; In conventional optical heads, a 1/2 wavelength plate is used for the rotation of the polarization plane of the light beam around the optical axis of the light beam, and a 1/2 wavelength plate is used for the difference between the polarization planes of individual semiconductor lasers. An additional device was required to separate the P-polarized light component and the S-polarized light component in equal proportions, such as a rotation adjustment mechanism for adjusting the rotation of the light beam with respect to the optical axis. In this embodiment, a non-polarizing beam splitter and a non-polarizing mirror are used as the beam splitter and the reflecting surface, so the polarization plane of the light beam from the semiconductor laser element 2 is
By rotating the polarizing beam split surface, which separates the light beam and makes it incident on the photodetector, by approximately 45 degrees with respect to the reference axis, that is, the Y axis, included in a plane parallel to the direction in which the light beam is transmitted, the P-polarized light component can be detected. Additional devices such as a 1/2 λ plate for separating the and S-polarized components in equal proportions and a rotation adjustment mechanism for adjusting the rotation of the light beam with respect to the optical axis are removed, making the device more compact and easier to assemble. and adjustment is simplified.

Recording, reproduction, and erasure of information on the tracks 14 of the optical disc 12 will be explained. When recording information on the optical disk 12, a magnetic field is generated from a magnet M provided on the side facing the optical head of the first disk 14, and the intensity is modulated according to the information to be recorded at a predetermined position on the track 14 on the recording surface. By being irradiated with a light beam, it is rapidly heated, the direction of magnetization is reversed, a bit p is formed, and information is recorded. Therefore, when no information is recorded on the optical disk 12, the direction of magnetization in the track 14 is aligned in a fixed direction. When erasing the information recorded on the optical disk 12, a light beam having a constant intensity greater than that during information reproduction is irradiated onto the track 14 while generating a magnetic field from the magnet M, and a light beam is formed on the track 14. Bit p is heated slowly and returned to the same state as when there was no information (inverted again)
.

When information recorded on the optical disk 12 is read out, a light beam of a certain intensity (weaker than the intensity at the time of erasing) is irradiated from the semiconductor laser element 4 onto the track 14 of the optical disk 12, and the light beam is emitted depending on the presence or absence of pits. The polarization plane of the beam is slightly rotated and reflected, and the beam is detected by a photodetector, which will be described later, to reproduce information. The light beam reflected from the optical disk 12 passes through the objective lens 20 again, is reflected by the reflective surface m of the prism 18, and is returned to the beam splitting surface 8 of the first beam splitter 6. The light beam is reflected at the beam splitting surface 8. Depending on the mounting direction of the semiconductor laser element 2, a light beam whose polarization plane is rotated by approximately 45 degrees with respect to the Y-axis is guided to the second polarization beam splitter 70. Polarizing beam splitter 7
0 is a combination of two right angle prisms, the joined surface of which is formed as a second beam splitting surface 74, and a second collimating lens 72 is provided on the side into which the light beam is incident. . The polarizing beam splitter 70 separates the light beam into two beams, and one beam is guided to the first photodetector 26 via the TTP 22 as a focus detection light beam. The other light beam is separated into an S-polarization component and a P-polarization component by a polarizing beam splitter 90, and the S-polarization component is reflected by a third beam splitter 90 and guided to a photodetector 28, where the light beam is divided into an S-polarization component and a P-polarization component. The P-polarized light component is passed through the beam splitter 90 and guided to the photodetector 27. By each photodetector,
The S-polarized component and the P-polarized component of the light beam are detected and subjected to predetermined processing by a signal processing circuit 30, which will be described later, to reproduce information recorded on the track 14 of the optical disc 12.

At the same time, a focus error signal FE and a tracking error signal TE are generated, and a focus control signal FC and a tracking control signal TC based on these FE and TE are supplied to the voice coils 32 and 34. 20, or the entire optical head is driven to maintain focusing and tracking.

2A to 2D show means for converting the cross-sectional shape of the light beam generated from the semiconductor laser device 2 shown in FIGS. 1A and 1B from an ellipse to a circle. In the example shown in FIG. 2A, the outer periphery of the collimating lens 4 is formed into a circular light shielding film or reflective film 80.
covered with. The light beam generated from the semiconductor laser element 2 is blocked or reflected by this light shielding film or reflective film 80, and is converted into a circular light beam having a diameter equal to the short axis of the ellipse. FIG. 2B shows an example in which an aperture 82 having a predetermined diameter is disposed between the collimating lens 4 and the semiconductor laser element 2. In this example, a light beam having an elliptical cross-sectional shape generated from the semiconductor laser device 2 is incident-limited by the aperture 82 and converted into a circular light beam having a size equal to the opening of the aperture 82. . This aperture may be formed integrally with the collimating lens 4 as shown in the M2D diagram. FIG. 2C shows an example in which the cross-sectional shape of the light beam is converted into a circular shape using only the collimating lens 4 and the semiconductor laser element 2. As is clear from the drawing, by arranging the collimating lens 4 close to the semiconductor laser element 2, the part of the light beam with large divergence, that is, the part that is wider than the short axis diameter of the elliptical light beam. is not incident on the lens 4, and only the light beam limited by the diameter of the lens 4 is collimated. Naturally, the light beam directed to the outside of the lens 4 is blocked by a lens support member (not shown), so that it does not become disturbance light.

Next, signal processing of the light beam detected by the photodetector will be explained. FIGS. 3A to 3C show 1A to 3C.
The beam projected onto the first photodetector 26 whose detection surface used in the optical head shown in FIGS. The relationship between the spot and the objective lens 20 when in focus and out of focus is shown.

When the objective lens 20 is in focus on the optical disc 12, spots Sa and sb as shown in FIG. 3B are projected onto the detection surface of the photodetector 26, which is divided into eight sections. The light beam that has passed through one glass plate of the TTP 22 is projected as a semicircular image on the photodetection areas a, b, g, and h, and the light beam that has passed through the other glass plate is projected on the photodetection areas C2d, e, It is projected as a semicircular image in the opposite direction to f. A dividing line α is placed approximately at the center of each image so that images with equal light intensity are projected onto the left and right photodetection areas.
β is placed. Therefore, when the outputs of the photodetection areas a-h are from ■ to ■, the dividing lines α and β indicate that the focusing error signal FE at the time of focusing is F E −1(■+■+■10)−( ■＋■10■10■Monthly〇It is arranged so that the conditions are met.

When the objective lens 20 moves away from the in-focus position with respect to the optical disc 12, smaller images Sa and Sb are projected onto the detection surface of the photodetector than when in focus, as shown in FIG. 3A. , the focusing error signal FE satisfies FE>0.

Furthermore, when the objective lens 20 approaches the in-focus position with respect to the optical disc 12, larger images Sa and Sb than when in focus appear on the detection surface of the photodetector, as shown in FIG. 3C. The focusing error signal FE becomes FE<0.

4A to 4C show a beam projected onto a first photodetector 26 whose detection surface is divided into eight sections, which is used in the optical head shown in FIGS. 1A and 1B. The relationship between the spot and the objective lens 200 when it is on track and when it is not on track is shown. The objective lens 20 is the optical disk 1
8 of the photodetector 26 when in focus with respect to 2.
Spots Sa and sb as shown in FIG. 4B are projected onto the divided detection surface. Parting lines u, v, and w are arranged approximately at the center of each image so that images of equal light intensity are projected onto the upper and lower photodetection regions.

Therefore, the dividing lines U, V, and W indicate that when the outputs of the photodetection areas a-h are ■ to ■, the tracking error signal TE on the combined track is T E −+(■+■10■+■)
−(■＋■＋■October month−〇) It is arranged so that the condition is satisfied.

When the objective lens 20 moves away from the in-track position with respect to the optical disc 12, smaller images Sa and Sb than when in focus are projected onto the detection surface of the photodetector, as shown in FIG. 4A. , the focusing error signal TE satisfies TE>0.

Furthermore, when the objective lens 20 approaches the in-track position with respect to the optical disc 12, the image Sa becomes larger than when in focus, as shown in FIG. 4C.

sb is projected onto the detection surface of the photodetector, and the focusing error signal TE becomes TE<0.

FIG. 5 shows a signal processing circuit for focusing and tracking of the objective lens 20 in the optical head of the present invention, and for reproducing recorded information. Objective lens 2
Focusing and tracking of 0 is controlled by processing a light beam detected by a first photodetector 26 whose detection surface is divided into eight detection areas and driving a voice coil. The outputs of detection areas a and f are added together by an adder circuit 40, and the outputs of detection areas d and g are added together by an adder circuit 42. These adder circuits 40 and 42
The output of is input to a differential amplifier 44 to generate a focusing error signal FE.

Further, the outputs of the detection areas c and h are added together by an adder circuit 50, and the outputs of the detection areas s and e are added together by an adder circuit 52. The outputs of the adder circuits 50 and 52 are input to a differential amplifier 54 to generate a tracking error signal TE.

The focusing error signal FE and tracking error signal TE are transmitted to the voice coil drive circuit 46, respectively.
and 56. Based on the focusing error signal FE and tracking error signal TH input to the drive circuits 46 and 56, the drive circuit 46 sends a signal to the voice coil 32 that controls the position of the objective lens 20 in the optical axis direction.
A focusing control signal FC and a tracking control signal TC are sent from the drive circuit 56 to the voice coil 34 that controls the position of the objective lens 20 in a direction perpendicular to the optical axis.
is supplied.

The focusing control signal FC and tracking control signal TC cause the respective voice coils 46 and 56 to
is driven, the objective lens 20 is maintained in the focused state and the focused track state, and the information recorded on the optical disc 12 is accurately reproduced.

Furthermore, reproduction of the recorded information is performed using the second and third photodetectors 27.
．． The light beam detected by 28 is processed and displayed on a display device or the like. The outputs from the photodetectors 27 and 28 are input to an adder 60, the output of which is the output when the objective lens 20 is tracked in focus and on track by the first photodetector 26. is processed by a reproduction signal processing circuit, and the information is reproduced by a display device or the like.

(Effects) According to the present invention, a 1/2 λ plate is used to keep the transmittance of the P-polarized component and the reflectance of the S-polarized component of the light beam constant, and a rotation adjustment mechanism that adjusts the rotation of the light beam with respect to the optical axis. The present invention provides an optical head that can be removed, provides stable detection characteristics with a simple configuration, and can be easily assembled in manufacturing. Furthermore, since it is possible to reduce the number of special parts for correcting the ellipse of the light beam, the number of parts forming the optical head is reduced, and an optical head that can be incorporated into a small and compact optical disk device is provided. .

[Brief explanation of drawings]

FIG. 1A is a schematic diagram showing the arrangement of components of an optical head incorporated in a magneto-optical optical disk device, FIG. 1B is a plan view of the optical head shown in FIG. 1A, and FIGS. 2A to 2D. 1A and 1B are schematic diagrams showing a method of converting the cross-sectional shape of the light beam generated from the semiconductor laser device 2 from an ellipse to a circular shape, and FIGS. 3A to 3C are A schematic diagram showing the relationship between the beam spot projected on the first photodetector 26 used in the optical head shown in FIG. 1A and FIG. 1B and the objective lens 20 when in focus and when out of focus; FIGS. 4A to 4 show the alignment of the beam spot projected on the first photodetector 26 used in the optical head shown in FIGS. 1A and 1B with the objective lens 20, and FIG. 5, a schematic diagram showing the relationship during platform tracking, is a block diagram showing a signal processing circuit for focusing and tracking of the objective lens 20 in the optical head shown in FIGS. 1A and 1B, and for reproducing recorded information. It is a diagram. 2... Semiconductor laser probe, 4... Collimating lens, 6... Beam splitter, 8.10... Beam split surface, 12... Optical disk, 14... Track, 16... Collimator Lens, 18... Reflection prism, 20... Objective lens, 22... TTP (2
parallel flat glass), 24... Naifetsuji, '2
6,28.66...Photodetector, 32.34...Voice coil, 70...Second beam splitter, 72.
...Collimating lens, 74... Beam splitting surface, 80... Reflecting surface, 82... Aperture, 90...
・Polarizing beam splitter

Claims (1)

[Claims] A light source that generates a light beam having a polarized plane, a transmission means that guides the light beam generated from the light source to an information recording medium, a focusing means that focuses the light beam on the information recording medium, and the information recording medium. in the information recording/reproducing apparatus, comprising: means for separating a light beam from the light source into at least two light beams; The plane of polarization of the light beam forms a predetermined angle, and the transmission means has a non-polarizing reflective surface, through which the light beam from the light source is directed to the focusing means. Information recording and reproducing device.